1. Field
Exemplary embodiments of the present invention relate to a method for operating a non-volatile memory device, and more particularly, to a reading method of a non-volatile memory device.
2. Description of the Related Art
Non-volatile memory device is capable of electrically performing program operation and erase operation without performing a refresh operation to reprogram data every predetermined cycle. Examples of such non-volatile memory devices include flash memory devices.
A non-volatile memory device generally includes plural memory cells, each having a stacked structure of a tunnel insulation layer, a floating gate, a dielectric layer, and a control gate. In the non-volatile memory device, a program operation and an erase operation are achieved by injecting or withdrawing electrons to or from a floating gate of a memory cell, through well-known Fowler-Nordheim (F-N) tunneling, and controlling a threshold voltage of the memory cell.
The non-volatile memory device has a problem of increasing a threshold voltage distribution width because the threshold voltage of the memory cell ascends as the number of erase/program operation cycles.
Such a concern is described in Korean Patent Publication No. 10-2010-0087806, which is referred to as Reference 1, hereafter. The Reference 1 provides one of solutions to reduce the above concerns.
The Reference 1 discloses a method including steps of applying a read voltage to the control gate of a selected memory cell, applying a relatively high pass voltage to the control gates of unselected memory cells adjacent to the selected memory cell, and applying a relatively low pass voltage to the control gates of the other unselected memory cells during a read operation. Furthermore, the Reference 1 discloses a method for producing a narrow the threshold voltage distribution width of a memory cell during a read operation despite the increasing number of cycles where the erase/program operation is performed.
As there is the growing level of the pass voltage applied to the control gate of the memory cell adjacent to the selected memory cell during the read operation, which is shown in the Reference 1, the vertical and horizontal electric fields applied to the selected memory cell increases. Accordingly, the floating gate of the selected memory cell might easily lose a lot of charges. The loss of charges grow worse, as more charges are captured in the floating gate of the selected memory cell and as the cycling is increased more.
In conclusion, limitation in the threshold voltage distribution width and prevention of the loss of charges in the read operation are in a trade-off relationship, and it may be difficult to reach both fulfilled conditions.